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Grumpy Cynic

Very slow progress recently. Between taking care of real income producing work, and other distractions, I'm STILL working on the vertical stab and rudder. A couple of the little details between the AV-361/45 and the AV-36 have required more 'blending' work than expected.
A 7 degree cant in the spar between the 2 versions means the operating rod mounts need to change by the same angle and the loads are not trivial due to the short arm at the hinge line and the need to deflect the rudder 45 degrees in one direction.

Grumpy Cynic

Thee is some confusion about the ordinates of the Wortmann FX 66H 159. I think I have this figured out now and hopefully this post will clear up some of the confusion about the various AV-36/361/362 airfoils.

There is the original AV-36 airfoil used by Fauvel. There are 2 versions of the ordinates floating around. One is nothing more than the original set with one batch of ordinates (lower IIRC) offset by one station. This is obviously from someones mistake in transferring the ordinates to electronic format.

This correct original AV-36/361 airfoil is "Fauvel original nose arcs".
It has a best L/D of 72 at around .47 CL and according to JavaFoil it still works, maybe even better, with dirt on it.
The maximum CL is around 1.7 at a pretty high alpha
It has a nasty bump as the CL goes up.

Smoothing the nose arc "Fauvel Smoothed nose" removes the nasty bump in the lift curve and ups the max L/D to 95 and raises the maximum CL to a little over 1.8. There is very little change in the moment or stall alpha.

Letting JavaFoil smooth the ordinates ups the max L/D to about 105 and the maximum CL to about 1.9.

Moving on to the Wortmann airfoil(s)
The ordinates provided by Falconair for the AV-362 "Wortmann from Falconair" are different than the ordinates labeled as being obtained from the university.
The Falconair version gives a max L/D of only 98 at a CL of around .87 which is little better than the smoothed AV-36 profile and at a much lower speed. It also has a maximum CL of only around 1.6. The drag rise as the speed lowers is not as "notchy" as the AV-36 profile but overall it doesn't seem like a very good option?

That leaves the last set of ordinates for the Wortmann FX 66H 159 with the notation from the university. It is visibly different than the Falconair version and has a much better L/D of about 196 at a CL of around .96 - or an even lower airspeed than any of the above. It also has a much lower max CL of only about 1.3 at a much lower stall alpha. JavaFoil also says that the L/D goes below any of the above when dirty.

The point of all this, for me, is that I see no reason to try to incorporate either version of the Wortmann airfoil, even though they were introduced to improve the performance of the AV-36/361. Unless there is real world evidence that the Wortmann airfoil actually increased the performance substantially I see no reason to do any more than smooth out the original flat bottom airfoil?

A completely different airfoil might work, but it would no longer be an AV-36/361

Grumpy Cynic

After watching another project here on HBA and the experience of the last couple of days learning just how much of Solidworks I don't know well enough I though this update is appropriate: .A Learned that the AV-36 plans/rights were available and thinking it was pretty close to what I was sketching - "Why not take a shortcut?"

B Made the deal and thinking "Just 6 weeks or a couple of months to redo the plans in modern CAD. After all I've already done this with another set of flying wing plans. How hard can it be?"

C The documentation arrives and I have had some time to look over what is there. Master plans are old copies and in poor shape. Get them digitized so I can work with them and think "This is going to be a little harder than the last project. Maybe 3 months?"

D What have I got myself into?! Dimensions are missing or scattered about on different pages. Some of the metal parts are so complex no modern builder will ever be able to duplicate them in a home shop! The landing manners of the AV-36 are obviously quite poor. The various modifications tried don't seem to have been effective. Still need a steerable nose gear for a powered version. The various owner modified AV-36s with power do little more than prove that it is possible - not that it is practical. The Germans have permanently grounded all of the AV-36C due to inflight failures!! Why? What needs to be fixed? No one has actually built an AV-362 with the Wortmann airfoil and the airfoil program says it is not a good match for this plane. So any hope of a significant increase in Lift to Drag is pretty poor. That leaves only the cleaned up Fauvel airfoil.I could have probably designed a lookalike flying wing from scratch faster than this project is progressing Adding power is going to add another layer of complexity and I'm still weeks from even being able to consider how.

E Where I think I'm at right now. Got a set of original French plans. I don't read/speak French but the copies are in much better shape and have some information not in the English version.The AV-36C had a modification to the wing that was unique to the AV-36C and is not in the plans. Reverse engineering the plans version indicates the plans built version structurally is OK, but just barely. Adding a proper steerable landing gear, with good manners, is proving to be possible and practical - with little increase in parts count or weight.I'm getting comfortable with some new Solidworks skills.I've started the process of converting the Solidworks files to 2D paper prints. Finding that "D" size prints are not big enough for some parts that should be printed full size for templates. This is a minor problem.........I think?Thanks to another HBA member the last little problem for the first choice power system has been solved. It may not be the ultimate power solution but it should be practical and reliable - after a reasonable development program.

I could still be on the D/K line to the left at the same altitude. At least I have a functional process in place....or so I think.

Grumpy Cynic

I have started work designing parts to replace the original rather complex set of parts for the removable outer wing panel with a folding wing mechanism. I decided it was best to know the loads involved, rather than try to reverse engineer the original parts. I used the Schrenk approximation method for this and the original gross weight and "G" load factor.
One rather surprising outcome is the curve for the local lift coefficient.* According to the curve the AV-361 should be prone to tip stall starting at about 80% of the span. However this has never been reported to be a problem. In fact the pilot reports all say that the handling of the AV-36 is "normal" to "good". I must conclude that other aerodynamic phenomena, like span-wise flow and limited elevator effectiveness, are offsetting this simple local lift coefficient calculation? For load calculations this isn't important as the overall lift distribution is the factor of interest.
I now have numbers from the spread sheet for loads to work with. Does not at this time account for wing inertia or point loads like the wing mount pins.

Grumpy Cynic

After some more math I can confirm that the 10G ultimate load Fauvel specified is accurate for the spar IF built with Fir. I have a note that he did approve the use of Sitka Spruce at some point but there was no mention of him reducing the "G" load limit or gross weight. Using 4700/9400 psi for Spruce reduces the ultimate "G" load to 8.38 at the outer wing separation span at 570 lbs gross for the AV-361.
8.3"G" with a FOS of 1.5 = 5.5"G" for a Spruce spar. There is about .65 ft^3 of wood in the spar caps.

Grumpy Cynic

Thought I'd worked up the DK curve closer to the little green asterisk. Maybe I have, but yesterday it sure felt like the project had slid clear back down the slope. Another post here on HBA gave me the bad news that we have lost one major source of aircraft grade wood here in the US. Being an all wood design, for now, that isn't welcome information.

The up side is that the work on designing a folding wing mechanism to replace the removable wing hardware, now in it's third iteration, only needs some details drawn and calculations triple checked before being finalized in CAD. Parts count is slightly increased but unlike the original removable wing hardware, the folding parts can all be built by the average builder or bought OTS.
Solo fold time, either way, by hand should be around 3 minutes per side..... less than 2 with an electric screwdriver. There will be one removable auxiliary hinge weighing around 1/4 pound, per side, that can be stowed in the fuselage.

The holiday season has also had a rather significant impact on progress. I'm the family's resident Grinch.

Grumpy Cynic

Trying to assemble the wing fold parts in a Solidworks assembly and things kept coming up with "over defined" error. Finally found the problem in a parent body where the bottom of the spar should have been 90 deg to the root rib, but was 90.03 degrees.
This wouldn't have been a problem with old school paper and "T" square but it is enough to mess up an electronic assembly.

After finally finding and "correcting" the bad sketch (after blowing up 2 generations of dependent bodies .... I was glad I keep backups) I double checked to make sure the angle was 90. It was better, but not 90.

SW said the spar bottom was now 90.00083+ degrees. Took the better part of an hour for this frustrated brain to figure out that I'd put the check sketch on the tapered front side of the spar, not the planar back side. Put the check sketch on the back side and the 90 degrees 'magically" appeared.

Grumpy Cynic

Just out of curiosity after thinking about this instead of sleeping last night:
Turns out I still have an error. Blaming it on rounding errors in SW now. Clicked up the precision on the dimensions and find the error is 0.00000002 degrees. Over the depth of the spar that is about 70 angstroms or 150 helium atoms.

A little more checking and some quick sketches it seems that SW has a "fudge limit" for mates of 0.00000005 (1x10^-7)degrees.

Grumpy Cynic

I have the fold mechanism locked down and the ailerons, with associated linkage, finished with part numbers assigned. After finishing the fold mechanism in detail and I'll move on to the rest of the outer wing. The attached spread sheets are samples of what I plan to provide with the final plans:

Grumpy Cynic

This weekend's project/decision:
The pic is of the auto-connect aileron socket. The diagonal tube can't be moved any further up. The blue oval is my potential collision conflict if the builder is off too much in their building accuracy. As show there is about .25" (6mm) clearance.*
My options
I'd like to make the dark, male, part of the socket with a longer lever so the size of the push/pull tube from this point to the fuselage linkage can be reduced. This means moving the pivot point down (Green oval), which I can do. But as show it is also in line with the locking pin which means that the whole assembly can be closer to the spar with a hollow pivot for locking pin clearance. Moving it down also means having to move it back some to clear the locking pin and again reducing the tube clearance. It helps - some.

Another option is to split the long push/pull tube into 2 halves. This means more parts to build/buy, but actually weighs less and costs less than one long tube.

A third option is to use a very short push/pull tube to connect to a truncated version of the original cable system - very much like the AV-45. This option costs more and weighs just as much as the dual tube system. The hybrid cable system still has the inherent problem of varying tension with changing environmental conditions. Given the Vd of the original is 137 mph a little slop could be a bad thing.

Note: As with several questions I've thought of asking here on HBA - by the time I go to the trouble of formulating a good question - the solution becomes much easier to figure out.

Don't know how much I'll get done this weekend - it's the granddaughter's Library Saturday so it is a short weekend for free time.

Edit: Realized after posting that the 2 part tube between the fold and the fuselage doesn't have to use a simple idle arm. The arm can be used to reverse the direction. Converting half of the tube to pull rather than push. Since the aileron loads are not symmetrical up/down there may be some weight savings to be found.

Grumpy Cynic

With a little bit of trial and error I managed to figure out how to build all of the aileron rods with the same size tube and thus eliminating a whole set of different sized parts. The only downside is that the shortest tube is now way over sized ...by almost an ounce. But to steal a quote from another builder "I can live with that" as a fair trade - same as the extravagant FOS of 1.8 for the other rods, rather than a more weight efficient 1.5.

I'll finish the mounts and bell-cranks another day. Still have lots of place holders in the CAD.

Grumpy Cynic

After a bit of TLAR* engineering of a couple of brackets, and modifying same because I discovered I used the wrong number for socket clearance on the bolt heads, I ran the result through SW sim. As expected it confirmed that TLAR isn't the best way to do things but in this case I lucked out. Just ended up with heavy parts, this one at 61 grams. At least it will be simple to fabricate - especially from CNC cut flat parts.

These were the last parts of the folding wing project to get finalized so now I need to clean up the CAD in preparation for drawings.

Grumpy Cynic

I've got the folding wing mechanism 'finished'. It works but I just don't like the aft spar pin....it isn't elegant. Moved on to the landing gear that will be needed for a powered version while my subconscious searches for a neater aft spar pin.

Putting the single main wheel where it needs to be meant moving/ redesigning the center mounted control system. That part of the project went pretty smoothly. Everything fits with original control forces and throws.

The retract mechanism for the landing gear has been sketched out and basic calculations done. However I've decided that for now the gear will be fixed. Just not enough time to do it all and I'd like to start building from plans this year. Structure needed for the retract mechanism will be included in the revised bulkheads so that a plans built version can be updated with as little work as possible.

My subconscious still hasn't found the elegant solution to the aft spar pins so I have moved on to the engine and mounts. I had originally planed on using my B+S 810 engine with a torsion-ally stiff drive shaft thinking it would weigh less than a soft system. But my estimates for the length was off. After getting everything in CAD the shaft turned out to be longer than expected. By the time it was large enough to turn the average prop of the needed diameter it weighed as much as a soft system will and the exhaust would have been a problem to plumb. Mounting such a large shaft would have been difficult. At least one AV-45 used a stiff system so it can be done.
The AV-36 was never designed for an engine and the AV-45 has a very different structure aft of the spar so a simple copy of the AV-45 method won't work. The AV-36/361 will need a more conventional welded steel mounting system.

The good news is that it looks like the CG isn't going to be as much of a problem as I was fearing. Designing a steel mount is going to take some thought if it is to remain light and easy to build.
3 steps forward 2 b
Pretty picture for the day:

Grumpy Cynic

After another nights sleep I've come to the conclusion I've been wasting time on trying to adapt the B+S 810 to the AV.

No one besides me would/should even consider this motor. It needs to be converted from vertical to horizontal. The factory mounting pads, while fairly easy to adapt to a normal firewall/engine mount configuration, just aren't suited to the AV which needs an extension shaft. A more practical solution would probably be an off the shelf horizontal shaft industrial engine - if one wants to use an industrial engine. I do have a Harbor Freight HZ V-twin setting at the shop. The ONLY advantage of the B+S 810 is that it can be inverted (still more work) leaving room above it for a BRS.

It seems I'm stuck in the same place a lot of others are. There just isn't a mass produced engine that is easily adaptable in the power and weigh range needed for the AVs. Paramotor power packages are light and powerful, but they still need to be adapted to function with an extension shaft. And a lot of people don't like the sound of 2 strokes. I know I don't so they aren't an option, for me. They may be the most practical solution?

The model turboprop that HBA member Arfang is working on is another option. That is more $'s than I, and probably others, would like to spend and the future availability is not secure.

From the start of this project I've thought that the ideal power package would be a hybrid electric one. Unfortunately I don't know of a developed system that could be bought mostly complete and adapted to the AV. If I go down this path that means developing one, and that takes time.

The point of all the? I'm at a point where I need to make a decision on the path forward. Options:

Forget the engine for now and just finish the plans for a glider version - but with some good hard points built in for future engine mounts. (not really an option for me personally)
Decide on an off the shelf motor to adapt and get on with the project.
Decide if the hybrid path is practical or more of a "want" of mine. If it makes sense from a cold dispassionate engineering point of view - am I prepared to spend the time to develop it?

I'm open to thoughts and opinions.............

Edit:
More questions:
Is the average home-builder going to be comfortable enough with the complexities of a hybrid system that they would consider installing and maintaining a package system?
We as a group seem to be getting comfortable with home-built avionics using Arduinos and Raspberries and open source software. To me, both seem equally simple. Are they perceived that way by others?

Grumpy Cynic

I've managed to make enough progress on the modern additions like the folding wing and hard points for the engine mount that it' time to start getting the prints part of the project started. The first step is to get the original Falconair prints for the AV-36/361 cleaned up and fully converted to AN-hardware and imperial material sizes.

The originals has several drawings scattered about the prints with no attached notes telling what they were. Part numbers are being added to help avoid such confusion.

From this point forward any plane or part built to specifications from the original prints will be refereed to as a 'Legacy AV-36/361'. Future versions built with the modern touches will be called AV-361 MkII or AV-361M MkII for ones with power.

Pretty pictures for the day:
Original print
Cleaned and updated with all change notices incorporated.

Grumpy Cynic

Found what I think is essentially a typo in the weight and balance section of the manual. By the time someone actually does a weight and balance they would probably figure it out, but it may cause some confusion at first. I'm posting my 'corrected' sheets for review just in case I'm the one that is really confused.

Grumpy Cynic

I now have the original builders manual restored and in digital form.
Still working on restoring and updating the prints.
You just don't realize how many parts there are to a 'simple' plane untill you try to assign part numbers and specifications to each.